FORCING terrorists to take lie detector tests to prove they are not planning another attack is "misguided" and would be a "waste of resources", according to an expert.

Professor Thomas Ormerod, head of the school of psychology at the University of Sussex, described the technology as "deeply flawed and potentially dangerous".

His comments come after the Justice Secretary was forced to defend plans to introduce "polygraph testing" which were announced by the Government as part of a wave of measures in the wake of the London Bridge attack.

The measures, described as a "major overhaul" in the way terrorists are punished and monitored, also include tougher sentences to see them locked up for longer.

Prof Ormerod, who has carried out a number of studies on polygraphs, including research for the FBI, said: "The proposal to use lie detector tests to monitor convicted terrorists or those on remand in the community is misguided.

"The results of polygraph testing are at best equivocal, and its scientific basis is questionable."

He said even in the hands of experienced experts, the results are only between "60 per cent and 80 per cent" reliable, which "on an individual testing basis is essentially useless".

"There also remains an open question as to whether motivated individuals can be trained to beat the test.

"In my view, the use of lie detector tests in this context will, at best, be a waste of police resources, and at worst will exacerbate problems associated with terrorism.

"Their use will give the public false confidence that they are being protected, while for terrorists who take and pass the tests, it gives them a free pass out of the legal system and cover to carry out attacks unimpeded."

When pressed on the accuracy of the tests, Justice Secretary Robert Buckland insisted lie detectors were important to identify "sleepers" - criminals who suddenly offend again after many years - and that they will not be the only measure used.

He told Sky News: "I'm not pretending on their own, polygraphs, lie detectors, are the be-all-and-end-all, which is why what we are also doing is doubling the number of specialised counter-terrorism probation officers... improving training, getting more psychologists in there, specialist imams as well will be working with these people."

Meanwhile, he told BBC Breakfast the proposal was "not a new concept", with detectors introduced about seven years ago to assess the risk posed to the public by sex offenders.

He insisted it was a "sensible measure in order to help maximise the understanding of the risks that some of these prisoners pose to society" which would not form part of a criminal investigation or evidence used in court.

But Prof Ormerod said the tests with sex offenders on licence were "opt-in trials" and "offenders were seeking support to help them manage their behaviour".

He said all the evidence from forensic psychology "points towards face-to-face investigative interviews as the only effective way of detecting deception".

Other experts questioned the credibility of polygraph tests, claiming there are ways of cheating to manipulate the results.

In the year to the end of September, there were 44 convictions for terrorism offences, with 17 offenders being sent to jail for between four and 10 years, the Government said.

Five were jailed for 10 years or more and one was handed a life sentence.

Around 245 convicted terrorists were freed from jail between 2012 and 2019.